The best companion plants for olive trees are those that share the olive’s preference for well-drained, drought-tolerant conditions while offering something in return: nitrogen for the soil, habitat for beneficial insects, or suppression of the fungal diseases that threaten olive groves. Legumes, aromatic herbs like lavender and rosemary, and certain flowering annuals all fit this description, though the reasons they work differ and so do the risks if you choose poorly. Picking the wrong neighbors, particularly vegetables in the nightshade or cucurbit families, can actually introduce a devastating soil pathogen that olive trees struggle to survive.
Flowering Plants That Protect Against Pests
One of the strongest research-backed reasons to plant companions near olive trees is biological pest control, specifically against the olive fruit fly and scale insects. A study of flowering ground covers in olive groves found that sowing patches of white mustard, coriander, borage, and crown daisy created habitat for both pollinating insects and parasitoid wasps that attack olive fruit flies and scale pests.1Agriculture, Ecosystems & Environment. Ground cover management with mixtures of flowering plants to enhance insect pollinators and natural enemies of pests in olive groves These parasitoid wasps lay their eggs inside pest larvae, killing them from within. Without flowering plants nearby to provide nectar and shelter, those wasps have little reason to stay in the grove.
The practical takeaway is that a mix of flowering species works better than a monoculture of one. Borage and coriander bloom at different times, for instance, which keeps beneficial insects fed across a longer season. You do not need to carpet the entire grove floor. Sowing or maintaining patches of these flowers between rows or along the edges is enough to see results. If you already have natural wildflower vegetation in your grove, selectively encouraging species like crown daisy rather than mowing everything flat can accomplish the same thing with less effort.
Legumes for Soil Nitrogen
Olive trees are not heavy feeders compared to fruit trees like citrus, but they still benefit from a steady nitrogen supply, especially on poor or rocky soils. Legume cover crops are the classic solution: clovers, vetches, medics, and lupins all pull nitrogen from the air and deposit it in the soil through their root nodules. Research on legume mulches in olive orchards confirmed that these cover crops increased soil nitrogen and improved both the nutritional status and yields of the olive trees compared to unfertilized natural vegetation.2Scientia Horticulturae. Soil nitrogen availability in olive orchards after mulching legume cover crop residues
There is a caveat worth knowing. That same research found the nitrogen boost was “slight and short-lived” relative to the amount of nitrogen contained in the legume biomass when it was mulched.2Scientia Horticulturae. Soil nitrogen availability in olive orchards after mulching legume cover crop residues In other words, legumes help, but they are not a miracle fertilizer. You will get a modest, ongoing trickle of nitrogen rather than a dramatic one-time dump. For most home growers or small-scale orchardists, that trickle is exactly what olive trees need. For large commercial operations on very depleted soils, legumes alone may not replace mineral fertilization entirely.
The choice of legume species also matters if you garden in a dry climate. Early-maturing legume varieties produce less biomass and fix less nitrogen, roughly 50 kilograms of nitrogen per hectare per year in above-ground tissue, but they finish their growing cycle earlier in spring and compete less with olive trees for water during the critical dry months.3Spanish Journal of Agricultural Research. Self-reseeding annual legumes for cover cropping in rainfed managed olive orchards Self-reseeding annual medics and subterranean clover are good candidates in Mediterranean or semi-arid conditions because they die back naturally before summer drought intensifies, then germinate again with fall rains without requiring replanting.
Aromatic Herbs Between the Rows
Lavender, rosemary, and lavandin are among the most popular companions planted between olive tree rows, and not just for aesthetics. A project across multiple olive orchards near Madrid planted aromatic shrubs between olive rows with the goals of diversifying farm income, preventing soil erosion, improving soil quality, and boosting biodiversity and pest biocontrol through enhanced ecosystem services.4ISHS Acta Horticulturae. Introduction of aromatic plants and beehives to enhance ecosystem services in traditional olive orchards Small apiaries were installed alongside the plantings, creating a dual-income system of olive oil and honey or aromatic herb products.
From a practical standpoint, lavender and rosemary share olive trees’ love of full sun, alkaline or neutral soil, and minimal irrigation. They establish deep root systems that help stabilize soil between rows, reducing erosion on sloped groves. Their fragrant oils attract pollinators while some growers believe the strong scent confuses or repels certain pest insects, though that claim is harder to pin down in controlled research than the pollinator benefit. Perhaps the most compelling reason to plant aromatics is economic: lavender and rosemary can be harvested and sold or distilled for essential oils, turning otherwise unproductive inter-row space into a second crop that generates income while the olive trees mature.
Alliums and Verticillium Wilt
Verticillium wilt, caused by the soil fungus Verticillium dahliae, is one of the most destructive diseases in olive cultivation, and it shapes companion planting decisions more than any other single factor.5MDPI Plants / Europe PMC. Verticillium Wilt of Olive and its Control: What Did We Learn during the Last Decade? The fungus persists in soil for years and attacks olive trees through the roots, clogging their vascular tissue until branches wilt and die. There is no reliable cure once a tree is infected, so prevention is everything.
This is where alliums, the onion and garlic family, get interesting. Field trials testing onion extract applied to olive trees found striking results: treated trees showed lower levels of the fungus in the soil, reduced oxidative stress in their leaves, and a meaningful increase in fruit fat content compared to untreated controls. In the same trials, irrigation with onion extract boosted the number of new shoots by about 148% and shoot length by roughly 54%.6MDPI / Plants (PubMed Central). Evaluation of the Biostimulant Activity and Verticillium Wilt Protection of an Onion Extract in Olive Crops (Olea europaea) The onion extract also increased root length by up to 37% in controlled conditions.6MDPI / Plants (PubMed Central). Evaluation of the Biostimulant Activity and Verticillium Wilt Protection of an Onion Extract in Olive Crops (Olea europaea)
These results come from extract applications rather than simply growing onions nearby, so planting a ring of garlic or onions around your olive tree is not guaranteed to replicate the same effect. Still, the sulfur compounds in allium roots are known to suppress soil-borne fungi, and interplanting garlic or chives near olive trees is a low-risk strategy that many experienced Mediterranean growers swear by. At worst, you harvest garlic. At best, you add a layer of protection against the one disease olive growers fear most.
What Not to Plant Near Olive Trees
Knowing what to avoid matters as much as knowing what to plant. The Verticillium fungus has a wide host range, and several common garden plants can harbor it and dramatically increase its population in the soil. The worst offenders are nightshades (tomatoes, peppers, eggplant, potatoes) and cucurbits (squash, cucumbers, melons). If you grow tomatoes between your olive trees one season and those tomatoes carry Verticillium, you may be seeding the soil with a pathogen that will threaten the olive trees for a decade.
Cotton and strawberries are also Verticillium hosts and should be kept well away from olive plantings. If you are establishing a new olive grove on land that previously grew any of these crops, the soil may already be contaminated. Some growers use soil solarization, covering the ground with clear plastic during the hottest months, to reduce fungal inocula before planting olives, but complete eradication is difficult once the pathogen is established.5MDPI Plants / Europe PMC. Verticillium Wilt of Olive and its Control: What Did We Learn during the Last Decade?
Grasses are generally safe companions and do not host Verticillium, but they compete aggressively with olive trees for water and nutrients. A dense turf lawn right up to the trunk of a young olive tree can stunt its growth more than you would expect. If you want a grassy ground cover, keep it mowed short and maintain a clear ring of bare or mulched soil around the tree’s drip line for the first several years.
Living Mulches and Weed Suppression
Beyond the specific companions discussed above, the broader concept of a living mulch, a low-growing ground cover maintained between and around trees, has strong research support in olive orchards. A comprehensive review of living mulch in fruit and olive orchards found benefits across multiple categories: suppression of unwanted weeds, increased biodiversity and soil fertility, enhanced microbial activity and nutrient cycling, improved soil structure and water retention, and support for beneficial insect populations.7SpringerLink / Agronomy for Sustainable Development. Living mulch in fruit and olive orchards. A review
Weed suppression is particularly valuable in olive groves because the alternative, repeated tillage or herbicide application, damages the shallow feeder roots olives develop near the soil surface and degrades soil structure over time. A living mulch of creeping thyme, white clover, or a native grass-legume mix shades out competing weeds while keeping the soil cooler and moister underneath. The allelopathic properties of certain cover crops add another layer of weed control: some species release chemicals from their roots or decomposing tissue that inhibit the germination of weed seeds.8Europe PMC. Allelopathy and its application as a weed management tool: A review
When choosing a living mulch, consider how aggressively the species spreads. A vigorous clover can become a weed itself if left unmanaged, climbing into the lower branches of young trees. Creeping thyme and prostrate rosemary stay low and tight, making them easier to control. In drier regions, sedum or low-growing ornamental grasses that go dormant in summer can fill the role without competing for water when the olive trees need it most.
Managing Water Competition
Water is the limiting factor in most olive-growing regions, and any companion you add will take some of it. This does not mean companion planting is a bad idea in dry climates, but it means you need to be strategic about species selection and timing. The research on self-reseeding annual legumes highlighted this trade-off clearly: late-maturing varieties fixed more nitrogen but competed harder for spring and early-summer water, while early-maturing varieties gave up some nitrogen benefit in exchange for finishing their lifecycle before the dry season peaked.3Spanish Journal of Agricultural Research. Self-reseeding annual legumes for cover cropping in rainfed managed olive orchards
If you grow olives on rainfall alone with no supplemental irrigation, prioritize companions that are either winter annuals (growing during the wet season and dying back in summer) or deeply drought-adapted perennials like lavender that establish their own deep roots and need minimal water once mature. Avoid lush, thirsty ground covers like white Dutch clover in these settings. In irrigated groves, the calculus shifts because you can afford to keep a more diverse understory alive through the summer, but even then, drip irrigation targeted at the olive trees rather than overhead sprinklers keeps the companion plants from stealing water meant for the trees.
Young olive trees are more vulnerable to water competition than mature ones. During the first three to five years after planting, keeping the area within a meter or so of the trunk free of companion plants gives the developing root system room to establish without competition. After that, the olive’s root network is extensive enough to coexist with moderate ground covers.
Biodiversity and Pollinator Networks
Olive trees are primarily wind-pollinated, so they do not strictly need bees and butterflies to set fruit. But the broader ecosystem around your olive trees matters more than you might think. Research on herb cover management in olive groves found that low-intensity ground cover, where vegetation is allowed to flower rather than being mowed or sprayed into submission, created complex and robust networks of interactions between floral visitors and plants.9Agriculture, Ecosystems & Environment. Intensive ground cover management and landscape simplification affect community-wide floral visitor-plant interactions in olive groves Those networks are not just nice for nature documentaries. They sustain the predatory and parasitoid insects that keep olive pests in check, as discussed in the pest control section above, and they support pollination of any companion crops you might also be growing for harvest.
The fungi living in olive tree roots add another dimension to companion planting. Olive trees form symbiotic relationships with mycorrhizal fungi that extend the tree’s root network and improve nutrient uptake, especially phosphorus. Research on olive root-associated microbiota has documented diverse communities of growth-promoting bacteria and fungi living in and around olive roots.10MDPI / Plants. Olive Tree Belowground Microbiota: Plant Growth-Promoting Bacteria and Fungi Companion plants that support rather than disrupt these microbial communities, particularly native ground covers and legumes that form their own mycorrhizal relationships, can strengthen the underground fungal network that benefits everyone growing in the grove.
Grazing Animals as Companions
Not every companion has to be a plant. In traditional Mediterranean olive farming, sheep have long served as living mowers and fertilizers, grazing the ground cover between trees, depositing manure, and keeping vegetation from competing too aggressively with the olives. Research comparing different ground cover management strategies in organic olive groves found that soils under sheep-managed cover held carbon levels comparable to those under lucerne cover crops.11Spanish Journal of Soil Science. Changes in the soil due to the use of sheep in cover crop management in organic olive groves The sheep essentially replaced mechanical mowing, added fertility through their manure, and generated income of their own through wool or meat.
This approach works best in groves with mature trees that have bark tough enough to resist nibbling. Young trees need protection, either individual trunk guards or temporary fencing that keeps the animals away from newly planted stock. Geese are sometimes used in smaller-scale operations for the same purpose, though they are less effective at handling woody weeds. If you are growing a legume or herb cover between your olive trees, timed grazing before the cover sets seed can keep it in check without the need for mowing equipment, while the animals spread the seeds and manure in a naturally random pattern that benefits soil health.
Can Companion Plants Shade Out Your Olives?
A meta-analysis of agroforestry systems in Mediterranean countries found that, on balance, trees reduced the yield of crops grown beneath them due to competition for light.12SpringerLink. Are agroforestry systems more productive than monocultures in Mediterranean countries? A meta-analysis That finding applies in reverse if you plant tall companions near olive trees: anything that shades the olive canopy will reduce its productivity. Olives are full-sun trees that produce less fruit and more vegetative growth when shaded.
In practice, this mostly rules out planting large shrubs or small trees on the south side of an olive (in the Northern Hemisphere) where they would block light. Fruit trees like figs or pomegranates can coexist at adequate spacing, say five to eight meters apart, because they occupy different canopy levels without heavily shading each other. But intercropping with tall crops like corn or sunflowers directly within the olive’s drip zone is a bad idea. The meta-analysis did note that under extreme heat or drought conditions, some degree of mutual shading might actually help by reducing water loss, though the overall trend was negative for crop yields.12SpringerLink. Are agroforestry systems more productive than monocultures in Mediterranean countries? A meta-analysis For most home growers, keeping companion plants low, below knee height for ground covers and herbs, waist height or lower for aromatics, avoids the light competition issue entirely.
Putting a Companion Planting Plan Together
If you are starting from scratch with a young olive tree or a new grove, a layered approach works well. Within the first meter of the trunk, keep the ground bare or lightly mulched with organic material for the first few years. Beyond that zone, sow a mix of an early-maturing annual legume like subterranean clover for nitrogen, a few patches of borage or coriander for beneficial insects, and a permanent planting of lavender or rosemary at the row margins for pollinator habitat, erosion control, and a secondary harvest. Add a few garlic or onion plants if Verticillium is a concern in your area.
As the trees mature and their root systems expand, you can bring the companion planting closer to the trunks. Creeping thyme makes an excellent living mulch under established trees because it suppresses weeds, tolerates foot traffic during harvest, and does not compete heavily for water. In commercial settings, a mowed or grazed clover-grass mix between rows keeps management simple while providing most of the soil health benefits the research supports. The key principle throughout is matching the companion’s water needs and lifecycle to your climate: if summers are bone dry, lean toward winter annuals and deeply drought-tolerant perennials. If you have irrigation, you can afford a more diverse and lush understory.